chore: monorepo scaffold, CI, MIT license

Bun workspaces (server/web/shared), typecheck+test gates, Gitea CI.
Refs PAI-90.

shared/src/types.ts

@@ -0,0 +1,4 @@
+import { z } from "zod";
+
+export const HealthResponse = z.object({ ok: z.literal(true) });
+export type HealthResponse = z.infer<typeof HealthResponse>;